The use of silicones as conditioning agents in cosmetic formulations is well known and widely documented in the patent literature. Generally, dispersed droplets of the silicone oil are suspended in the composition, which is then applied to the hair to deposit the silicone material on the hair shaft.
A typical method of silicone shampoo manufacture is disclosed in WO 92/10162. Essentially, the silicone material is emulsified directly into the shampoo by an in situ hot process, in which the complete shampoo mixture incorporating the silicone is mixed thoroughly at elevated temperature, pumped through a high shear mill and then cooled. The silicone can be dispersed in a first process stage with anionic surfactant and fatty alcohol to form a premix. The premix is then mixed with the remaining materials of the shampoo, pumped through a high shear mill, and cooled to obtain the final composition.
A disadvantage associated with an in situ hot process such as is described in WO 92/10162 is that factory handling of viscous silicone oil is difficult in the context of a full shampoo manufacturing operation.
A further disadvantage is that special equipment is normally needed to control silicone particle size during manufacture. GB 2 170 216 A discloses a similar process, in which the full shampoo composition incorporating insoluble, non-volatile silicone is sheared with a high shear mixer until the silicone particles are on average less than 2 microns in diameter. The particle size distribution is then said to be from about 2 to about 55 microns.
In order to solve the above mentioned problems with in situ hot processing of silicone, the alternative of incorporating the silicone as a preformed aqueous emulsion has been proposed. Such a method has the consequences that the silicone is incorporated with a predeterminable, controllable particle size distribution. The silicone is insoluble and remains emulsified in the fully formulated shampoo composition, and thus the step of high shear processing of the silicone within the fully formulated shampoo composition is not required. This also makes manufacture of the compositions easier.
A typical method for incorporating insoluble, non-volatile silicone materials into a conditioning shampoo is disclosed in U.S. Pat. No. 5,085,857 in which such materials are incorporated in the shampoo composition as a pre-formed aqueous emulsion of average particle size less than 2 microns. All the ingredients are mixed in a simple hot or cold process in which the average particle size of the silicone material in the emulsion remains the same in the final shampoo composition. Preferably, this size is from 0.01 to 1 micron, e.g. 0.4 micron.
EP 0 529 883 A1 discloses hair shampoo compositions made by an equivalent method and comprising microemulsified particles of silicone having a particle size of 0.15 microns or less, e.g., 0.036 microns. Reducing the silicone particle size still further in this way is said to improve stability, optical properties and conditioning performance.
A problem encountered with these small particle size silicone formulations is that the conditioning performance may be insufficient for many people, particularly in regions such as Japan and South East Asia where consumers desire a high level of conditioning and a "weighty" feel to their hair.
We have now found that the conditioning performance of small particle size emulsified silicone in a surfactant-based shampoo composition can be significantly boosted by the inclusion in the shampoo composition of an amino functionalised silicone.
U.S. Pat. No. 5,198,209 (Amway Corp) and L'Oreal EP 0 811 371 disclose conditioning shampoos with cleansing surfactant and a combination of dimethicone and trimethylsilylamodimethicone. The exemplified compositions use dimethicone fluid such as DC200 (60,000 cst). The dimethicone fluid is added directly to the shampoo as neat silicone oil of unspecified silicone particle size.